There is presently known, as disclosed in U.S. Pat. Nos. Re 27,653 and 3,857,631, an outside rear view mirror for an automobile which is electrically adjustable by means of a remote control switch provided within the automobile. The apparatus has a mounting plate for mounting a mirror thereon, and the mounting plate is mounted on a support by means of a universal joint, so that the mounting plate can be adjusted around two mutually perpendicular axes relative to the support. On the support is provided a single reversible electric motor and a transmission system having two planetary gear transmissions, each having a sun pinion wheel and planet wheel meshed with the sun wheel. The sun wheels of the planetary gear systems are disposed coaxially with the motor shaft, and an electromagnetically controlled coupling selectively couples the motor to one or the other of the two pinion sun wheels. Pulleys are driven by the sun and planet wheel systems and are connected to the mounting plate for the mirror by two strings, one for each pulley, the strings being laid in a loop around the pulley, guided around guide pulleys, and connected to the mounting plate at mutually opposed points located on the mounting plate in pairs. One end of each string is held on the mounting plate by a spring, and the other end is connected directly to the mounting plate.
As pointed out above, this known apparatus has two tensioning springs and two strings, one for applying a force for achieving pivoting motion around each of the axes of rotation.
A disadvantage of this construction is that when constructing the apparatus, each string must be provided with a ferrule f.i. made of copper at both ends thereof, which ferrule has to be pinched onto the end of the string at exactly the correct position, and will be located in a cavity in the mounting plate or at the outer end of the respective spring.
Moreover, the active part of each of the strings must have exactly the correct length, which makes the assembly of the strings and mounting plate more difficult and time-consuming.
After the apparatus with the two strings and two springs has been assembled, it still has some other disadvantages. Among these are:
(1) The apparatus is direction-sensitive. This means that the forces for adjusting the mirror around one adjusting axis are not equal for adjustment in the opposite directions. This is true for mirror adjustments around each of the two adjusting axes. If one pushes first in the middle of one edge of the mounting plate, at which point one end of one string is directly fixed to said mounting plate, and thereafter in the middle of the opposite edge, at which point the other end of the one string is fixed to the outer end of the tensioning spring, the force which must be applied in the first instance for tilting the mounting plate is 1.5-2 times less than the force which must be applied in the second instance.
For adjusting the mirror or the mounting plate respectively in this way, the string must slip over one of the pulleys of the planetary gear systems. The less the smaller of the above two mentioned adjusting forces, the sooner the mirror mounted on a car will flutter or inadvertently take another position.
(2) The adjusting force in both directions decreases equally as the temperature falls to -25.degree. C, a temperature to which cars can be subjected in normal practice. In such a normal range of temperature conditions, at the low end of the range, the lower value adjusting force appears to be capable of decreasing to a value which is relatively near zero, indicating that the friction of the strings over the pulleys for one sense of adjustment has disappeared almost completely. In such a case, the adjusting apparatus is operative only in one direction around the adjusting axes.